Qantas, the Australian airline widely considered to be the world's safest, has flown a jet partly fueled by modified cooking oil.

The 300-seat Qantas Airbus A330 that undertook the commercial flight between the Australia east coast city of Sydney and Adelaide, in the country's south, used a 50:50 mix of conventional fuel and refined cooking oil, according to the Australian Broadcasting Corporation.

The same fuel had been used "successfully" in a six-month, 1,200 flight trial by Lufthansa between Hamburg and Frankfurt.

Crikey.com reported that Qantas was using the flight to boost its "green credibility" as it seeks to jointly invest in aviation fuel making plants in Australia with US firms Solena and Solyzene. The plants would use recycled waste and algal products.

The oil being used in one of the A330’s engines was not a food crop, Crikey cited the carrier as saying, but rather a blend of aviation kerosene and waste cooking oil derived kerosene that Dutch firm SkyNRG produced for the Lufthansa trial.

The ABC reports the biofuel cost four times more than conventional fuel, partly because it was imported from the United States — having been refined in Houston before being shipped to Australia.

But Qantas said it was absorbing the cost because it was keen to highlight the need for an Australian biofuel source.

Crikey cited Joe Ozimek, a senior Boeing executive reportedly pushing Australian carriers to buy the fuel — called 737 MAX — said that with every barrel of biofuel that was produced, the price would fall.

Airlines have been developing biofuels to try and minimize their exposure to rising oil prices and carbon emission charges, according to the Australia News Network.